An active frequency separating circuit is known (German Patent DE-PS 38 02 810) which has the advantages that, to a large extent, a deleterious capacitive loading is avoided for AM-band signals, and that the active components of FM and AM amplifiers are affected only insignificantly by signals in the respective other range. It has been found, however, that the AM amplifier of the known active frequency separating circuit diminishes the FM signal somewhat because the adaptor circuit of the FM amplifier is conventionally provided with a series inductance at its input which, together with the three series-connected capacitors, forms a series resonance circuit. Since the center one of the three capacitors has the lowest capacitance value, the high voltage or reference point of the series resonance circuit is located between the center capacitor and said inductance. Because of the high impedance of the high reference point, the FM (Ultra-Short-Wave) signal experiences weakening even, at low loads.